/* arcfour.c --- The arcfour stream cipher
 * Copyright (C) 2000, 2001, 2002, 2003, 2005, 2006 Free Software
 * Foundation, Inc.
 *
 * This file is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published
 * by the Free Software Foundation; either version 2, or (at your
 * option) any later version.
 *
 * This file is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this file; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 */
/** @file lib/arcfour.c
 * @brief Arcfour (RC4-compatible) stream cipher implementation
 *
 * Code from Libgcrypt adapted for gnulib by Simon Josefsson.
 *
 * For a description of the algorithm, see:
 * 
 *   Bruce Schneier: Applied Cryptography. John Wiley & Sons, 1996.
 *   ISBN 0-471-11709-9. Pages 397 ff.
 */

#include "arcfour.h"

/** @brief Encrypt using Arcfour stream cipher
 * @param context Context structure
 * @param inbuf Input buffer
 * @param outbuf Output buffer
 * @param length Number of bytes in @p inbuf
 *
 * Copies from @p inbuf to @p outbuf, encrypting (or decrypting) using
 * the stream controlled by @p context.
 */
void
arcfour_stream (arcfour_context * context, const char *inbuf, char *outbuf,
		size_t length)
{
  uint8_t i = context->idx_i;
  uint8_t j = context->idx_j;
  char *sbox = context->sbox;

  for (; length > 0; length--)
    {
      char t;

      i++;
      j += sbox[i];
      t = sbox[i];
      sbox[i] = sbox[j];
      sbox[j] = t;
      *outbuf++ = (*inbuf++
		   ^ sbox[(0U + sbox[i] + sbox[j]) % ARCFOUR_SBOX_SIZE]);
    }

  context->idx_i = i;
  context->idx_j = j;
}

/** @brief Initialize an @ref arcfour_context
 * @param context Context structure
 * @param key Key data
 * @param keylen Length of key
 *
 * Initializes @p context using @p key.
 */
void
arcfour_setkey (arcfour_context * context, const char *key, size_t keylen)
{
  size_t i, j, k;
  char *sbox = context->sbox;

  context->idx_i = context->idx_j = 0;
  for (i = 0; i < ARCFOUR_SBOX_SIZE; i++)
    sbox[i] = i;
  for (i = j = k = 0; i < ARCFOUR_SBOX_SIZE; i++)
    {
      char t;
      j = (j + sbox[i] + key[k]) % ARCFOUR_SBOX_SIZE;
      t = sbox[i];
      sbox[i] = sbox[j];
      sbox[j] = t;
      if (++k == keylen)
	k = 0;
    }
}
